This invention relates to fuel injection control for a diesel engine adapted to trap particulate matter contained in exhaust gas discharged from the diesel engine.
Tokkai 7-11935 published by the Japanese Patent Office in 1995 discloses a filter for particulate matter (hereinafter referred to as particulate filter) which traps particulate matter contained in exhaust gas from a diesel engine of a vehicle. Particulate matter may also be termed smoke.
Generally a diesel engine operates at a lean air fuel ratio, in other words, at an excess air factor which is greater than unity. When large amounts of particulate matter are deposited in the particulate filter, the deposited particulate matter is combusted by controlling the fuel injection amount to increase the exhaust gas temperature of the engine so that the excess air factor is approximately equal to one. This operation is termed regeneration of the particulate filter.
Immediately before regeneration of the particulate filter, a considerable amount of particulate matter has been deposited in the particulate filter. The particulate matter deposited in the particulate filter increases the flow resistance to the exhaust gas. The increase in the exhaust gas resistance increases the exhaust gas pressure and as a result the intake air amount of the engine decreases. This decrease in the intake air amount causes a reduction in the output torque of the engine, particularly in fully loaded operating regions. A fully loaded operating region is an operating state in which an accelerator pedal of the vehicle is fully depressed.
It is therefore an object of this invention to reduce the effect of particulate matter deposits in the particulate filter on the output torque of the engine.
In order to achieve the above object, this invention provides a fuel injection control device for such a diesel engine that comprises an exhaust passage discharging exhaust gas produced by combustion of a mixture of fuel and air, and a particulate filter trapping particulate matter contained in the exhaust gas.
The device comprises a fuel injector injecting fuel, a sensor detecting a required output of the diesel engine, a sensor detecting an intake air amount of the diesel engine, a sensor detecting an operation condition of the engine, and a programmable controller controlling a fuel injection amount of the fuel injector to a target fuel injection amount.
The controller is programmed to calculate a basic fuel injection amount based on the required output, calculate a maximum fuel injection amount in response to the intake air amount, determine based on the operating condition whether or not a deposited amount of the particulate matter on the particulate filter has exceeded a predetermined amount, increase the maximum fuel injection amount when the deposited amount of the particulate matter has exceeded the predetermined amount, and set the smaller of the basic fuel injection amount and the maximum fuel injection amount as the target fuel injection amount.
This invention also provides a fuel injection control method for such a diesel engine that comprises an exhaust passage discharging exhaust gas produced by combustion of a mixture of fuel and air, a fuel injector injecting fuel and a particulate filter trapping particulate matter contained in the exhaust gas.
The method comprises detecting a required output of the diesel engine, detecting an intake air amount of the diesel engine, detecting an operation condition of the engine, controlling a fuel injection amount of the fuel injecting means to a target fuel injection amount, calculating a basic fuel injection amount based on the required output, calculating a maximum fuel injection amount in response to the intake air amount, determining based on the operating condition whether or not a deposited amount of the particulate matter on the particulate filter has exceeded a predetermined amount, increasing the maximum fuel injection amount when the deposited amount of the particulate matter has exceeded the predetermined amount, and setting the smaller of the basic fuel injection amount and the maximum fuel injection amount as the target fuel injection amount.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.